Our U.S. Pat. No. 3,819,536 issued June 25, 1974 for "Process for Preparing a Catalyst Based on Ruthenium" and our U.S. Pat. No. 3,835,069 issued Sept. 10, 1974 for "Ruthenium Catalyst System" disclose ruthenium catalysts which are protected from volatilization under oxidizing conditions. These two patents teach stabilization of a ruthenium catalyst system by use of alkaline earth materials or rate earth materials in order to provide some protective agent for the ruthenium under oxidizing conditions. The patents teach two different methods of developing the stabilized ruthenium compound. The patents also teach that under reducing conditions, the catalyst become active in its role of eliminating oxides of nitrogen but under oxidizing conditions, the alkaline earth or rare earth materials do combine with the ruthenium to form compounds which are not generally volatilized.
The present application teaches a method of preparing a stabilized ruthenium catalyst system, no matter how the catalyst system is laid down on the catalyst substrate, which has a stability at extremely high space velocity (100,000 hours .sup.-1 and higher) and at temperatures in excess of 750.degree. C. The stabilized catalyst system may be applied to a substrate as described in either of the above-identified U.S. patents. The principal factor for achieving the higher stability of these catalysts comes from the substitution of a portion of the ruthenium of the catalyst system by a stable base metal oxide of a valence state which permits formation of a perosvskite type compound when the base metal oxide is present with a stabilizing metal oxide, ruthenium and oxygen.